... optional 3.Apply to all kinds of medium 4.CE.UL.RoHS.ISO Explosion-proof ultrasonic level meter for distance ... dust, smoke, electromagnetic interference, strong corrosion etc. Widely used in chemical, petroleum, metallurgy, coal, building materials, paper making, ... protection industry and so on. Ultrasonic can spread effective in lots of occasion, Such as: storage tank, materials trough, pool ...